How ESTL and ESA are establishing a structured approach to introducing new fluid lubricants into space mechanisms.
Why do we need new space lubricants?
For decades, the space industry has relied on a relatively small selection of established oil and grease products. These lubricants have extensive flight heritage, providing confidence in their performance across a wide range of spacecraft mechanisms.
However, established products do not meet every technical requirement. Demands for longer operating life, higher temperatures, improved boundary lubrication performance and stringent contamination control can make lubricant selection challenging. There is also growing uncertainty surrounding the long-term availability of some established fluorinated materials, including PFPE lubricants, due to proposed environmental restrictions.
Meanwhile, new lubricant formulations, alternative thickener technologies and entirely new base oil chemistries are being developed, offering potential benefits for future space applications. But this presents an important question for the space industry:
How can we demonstrate that a new lubricant is suitable for use in a spacecraft mechanism when it lacks the extensive heritage of established products?
Establishing a clear route for new lubricants
To address this challenge, the European Space Agency (ESA) tasked ESR Technology’s European Space Tribology Laboratory (ESTL) to develop a structured set of guidelines defining the verification and validation data expected when introducing new fluid lubricants into ESA-overseen programmes. The resulting document, Guidelines for Qualification of New Fluid Lubricants, was formally released in April 2025, following a campaign of feedback from industry and practical experience from ESTL.
This document establishes the expectations for the introduction of new fluid lubricants into relevant mechanism development and qualification programmes. The guidelines are intended to remove uncertainty around the evidence required, helping engineers and manufacturers understand what needs to be demonstrated, what data needs to be available, and when it needs to be reviewed.
What do the guidelines cover?
The guidelines establish a structured process covering two key activities: lubricant verification and lubricant validation.
- Verification: Is the lubricant product consistent and properly characterised? Before a lubricant can be considered for a particular application, there needs to be objective evidence of its properties and manufacturing consistency. The guidelines identify the data needed to characterise a lubricant and establish appropriate controls for future production. Depending on the product, this includes properties such as viscosity, density, evaporation, grease consistency, oil separation and contamination. Space-specific considerations, including outgassing, vapour pressure and tribological behaviour, are also addressed. The process helps establish a reliable body of product data and appropriate acceptance criteria, giving engineers a sound basis for comparing candidate lubricants and assessing their suitability against the requirements of a particular mechanism.
- Validation: Is the lubricant suitable for its intended operating environment? Characterising a lubricant is not enough to demonstrate that it will perform as required in space. Validation therefore involves testing a verified lubricant to provide objective evidence of its suitability under the relevant operating conditions. Depending on the application, this may include tribometer testing and component-level assessments under thermal vacuum conditions, covering relevant temperatures, contact stresses, speeds and lubrication regimes. Other tests may be required to address specific environmental or material compatibility concerns. The validation programme is defined according to the intended application, with the scope and extent of testing agreed between the mechanism supplier and the relevant Agency. The guidelines establish when the necessary evidence should be available during mechanism development, helping ensure that outstanding data requirements are identified and addressed before the mechanism proceeds into its qualification test campaign.
An important distinction: lubricants are not qualified in isolation
One of the important principles underpinning the guidelines is the distinction between lubricant verification, lubricant validation and mechanism qualification. In accordance with European Cooperation for Space Standardization (ECSS) terminology, materials are validated, processes are verified, and mechanical parts are qualified.
A lubricant may have extensive experience in successfully qualified mechanisms, but this does not automatically mean that it is suitable for every subsequent application. Different mechanisms may impose different operating temperatures, contact stresses, speeds, lifetimes and environmental requirements. Evidence of successful performance in one application can reduce risk in another, but it does not eliminate the need to assess suitability for the intended application. The guidelines therefore define the minimum prerequisite steps and the expected availability of data before a new lubricant is introduced into a mechanism qualification campaign. Successful mechanism qualification then provides the final application-specific evidence of suitability.
What does this mean for lubricant manufacturers?
The guidelines are not just relevant to mechanism designers. For lubricant manufacturers developing new products for the space market, they provide a valuable framework for understanding the technical evidence expected to support adoption of a new oil or grease.
A promising formulation, attractive laboratory results or a compelling set of material properties will not, by themselves, establish suitability for space mechanisms. Manufacturers need to consider how the product will be characterised, how manufacturing consistency will be demonstrated, what verification data will be available, and how the lubricant’s performance will be validated for its intended operating environment.
Addressing these questions early can help manufacturers plan their development programmes, anticipate testing requirements and provide the information needed by prospective customers. For mechanism engineers, the same framework provides a more consistent basis for assessing new lubricant candidates, identifying data gaps and planning the activities required before a lubricant can be incorporated into a qualification programme.
Supporting the next generation of space lubricants
At ESTL, we recognise the importance of enabling new lubricant technologies while maintaining the rigorous evidence base required for reliable spacecraft mechanisms. The Guidelines for Qualification of New Fluid Lubricants provide a common framework for lubricant manufacturers, mechanism engineers and customers to work towards that objective.
Interested in developing a new space lubricant or selecting one for your next mechanism?
The Guidelines for Qualification of New Fluid Lubricants, are available through the Members Area of the ESTL website.
For more information about ESTL’s space tribology expertise, lubricant testing and support for the development and assessment of new lubricants, please get in touch.